Condense-luminescence and global characterization of metal particle suspension combustion

Abstract

Thermal processing of aluminum (Al) particles such as annealing followed by rapid quenching had been previously shown to affect single metal particle burning rates. This study extends single particle combustion to a global material-based energy exchange model. Experiments were designed to investigate the global energy exchange resulting from Al powder suspensions processed to induce different (fast and slow) burning regimes. Thermally processed and untreated Al particles were reacted as suspended powder in a closed bomb calorimeter. The calorimeter monitored the transient temperature changes resulting from energy release upon powder combustion. The product residue was analyzed for species concentration using X-ray diffraction. Results link the phase fractions of the aluminum oxide combustion products with global radiant fluxes in the calorimeter system. Metastable alumina associated with nano-oxide formation is in substantially higher concentration for thermally processed powder reactions and also produces greater energy transfer rates. The increased energy transfer rates correspond to higher radiant energy emission which may result from condensation energy associated with nano-oxide particle formation. This study qualifies condense-luminescence as a means for increasing the energy release rates of aluminum particles. By strategically altering metal fuels to control formation of nano-oxide particles upon combustion, appreciable increases in the radiant energy flux can transform energy release rates.